Shaped polymeric shield against neutron and gamma radiation

ABSTRACT

A polymeric material having a shielding effect against radiation is provided in the form of a shaped body which may be a plate, flexible sheet, or of any other desired shape, which body consists essentially of a synthetic plastic material including synthetic rubber, or of natural rubber, having distributed therethrough and intimately mixed therewith an effective amount of at least one compound of a saturated fatty acid being solid at room temperature and having at least 9 carbon atoms with at least one metal selected from the group consisting of lead, bismuth, tungsten, zirconium, iron, tin, cadmium, lithium and barium.

United States Patent [72] Inventor Reinhard Ernst Vogel Munich,iiarlaching, Germany [21] Appl. No. 758,107

[22] Filed Sept. 6, 1968 [45] Patented Sept. 28, 1971 [73] Assignee Friedrich Marxen Vaduz, Grand Duchy of Liechtenstein, a part interest Continuation-impart of application Ser. No. 596,764, Nov. 25, 1966, now Patent No. 3,434,978.

[54] SHAPED POLYMERIC SHIELD AGAINST NEUTRON AND GAMMA RADIATION 851,602 10/1960 GreatBritain Primary Examiner-James W. Lawrence Assistant Examiner-Morton J. Frome Attorney-Michael S. Striker ABSTRACT: A polymeric material having a shielding efi'ect against radiation is provided in the form of a shaped body which may be a plate, flexible sheet, or of any other desired shape, which body consists essentially of a synthetic plastic material including synthetic rubber, or of natural rubber, having distributed therethrough and intimately mixed therewith an effective amount of at least one compound of a saturated fatty acid being solid at room temperature and having at least 9 carbon atoms with at least one metal selected from the group consisting of lead, bismuth, tungsten, zirconium, iron, tin, cadmium, lithium and barium.

SHAPED POLYMERIC SHIELD AGAINST NEUTRON AND GAMMA RADIATION CROSS-REFERENCE TO RELATED APPLICATIONS The present application is a continuation-in-part of my copending application Ser. No. 596,764, filed Nov. 25, 1966 now Pat. No. 3,434,978 and entitled Building Material having a Shielding Effect Against Radiation and Method of Making the Same, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION In my above-mentioned copending application it has been disclosed that cementitious building materials may be endowed with a shielding effect against radiation by incorporating in the cementitious material and finely and intimately distributing therethrough an effective amount of at least one compound of a saturated fatty acid which is solid at room temperature and has at least 9 carbon atoms with at least one metal selected from the group consisting of lead, bismuth, tungsten, zirconium, iron, tin cadmium, lithium and barium.

Preferably, the saturated fatty acid has at least 16 carbon atoms and very good results are achieved with palmitic acid or stearic acid or a montanic acid as the fatty acid. It has also been found very desirable to utilize compounds selected from the group consisting of lead compounds of stearic and montanic acids.

It has also been suggested in the above-mentioned applica-,

tion to additionally incorporate in the cementitious material an effective amount of at least one substance selected from the group consisting of barium oxide, boron carbide, boric acid, boron trioxide, iron, lead sulfide, and lead oxide.

Surprisingly, it has been found that substantially the same fatty acid compounds as described in the above-mentioned mentioned application may also be incorporated in certain polymeric materials in order to endow such polymeric materials with a shielding effect against radioactive radiation as well as against alpha, beta, gamma, ionic and neutron radiation.

It is an object of the present invention to provide polymeric compounds, preferably in the form of shaped bodies such as for instance plates, coatings or flexible sheets which will possess such shielding effect against radioactive radiation, and also to provide a method of producing such shielding bodies.

SUMMARY OF THE INVENTION According to the invention, a shaped body having a shielding effect against radioactive radiation, and particularly against gamma and neutron radiation is provided which shaped body consists essentially of material selected from the group consisting of natural and synthetic rubbers and synthetic plastic materials, having distributed therethrough and intimately mixed therewith an effective amount of at least one compound of (a) a saturated fatty acid being solid at room temperature and having at least 9 carbon atoms, with (b) at least one metal selected from the group consisting of lead, bismuth, tungsten, zirconium, iron, tin, cadmium, lithium and barium.

According to a preferred embodiment of the present invention, the shaped body additionally includes a finely subdivided boron compound.

The synthetic plastic material is preferably selected from the group consisting of polyurethanes, polyamides, polyethylene, polyfluoroethylene, polypropylene, epoxy resins, unsaturated polymerizable polyesters and synthetic rubbers.

It is also within the scope of the present invention, to utilize as the synthetic plastic material polyvinyl chloride, polyvinyl fluoride, copolymers of polyvinyl fluoride and polyvinyl chloride, polystyrene and copolymers thereof, and polymethacrylates.

Of the synthetic rubbers, it is particularly preferred to utilized polyisobutylene, butadiene-styrene polymerizates, chloroprene, and alkyl-polysulfides.

Preferably the effective amount of the compound of the saturated fatty acid will be equal to between about 5 and 60 percent of the weight of the shaped body, and most preferably it will be equal to between about 10 and 40 percent of the weight of the shaped body.

According to certain preferred embodiments of the present invention, the shaped body additionally includes effective amounts of at least one finely subdivided substance selected from the group consisting of lead and lead compounds, tungsten and tungsten oxides, iron and iron compounds, boron and boron compounds, cadmium, cadmium oxide and cadmium sulfide. Some of these suitable compounds are described in some more detail in my above-mentioned copending application the contents of which are included herein by reference.

Preferably, the additional finely subdivided substance is of colloidal particle size. Suitable boron compounds include boron carbide, boric acid and boron trioxide.

Preferably, the shaped body of the present invention is formed by first producing an intimate mixture of the fatty acid compound and of the synthetic material or natural rubber in polymerizable and thus hardenable form, followed by subjecting the thus-formed mixture to polymerization of the polymerizable component thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As briefly described above, fatty acid compounds with certain metals, specifically compounds of fatty acids being solid at room temperature and having at least 9 carbon atoms, with at least one metal selected from the group consisting of lead, bismuth, tungsten, zirconium, iron, tin, cadmium, lithium and barium may be incorporated into a great number of synthetic rubbers in order to endow bodies formed thereof with an effective shielding effect against radioactive radiation as well as against alpha, beta, gamma, ionic and neutron radiation.

Of these types of radiation, gamma rays and neutrons are the most dangerous ones. Gamma rays are primarily absorbed by elements of high density and a high number in the periodic system, whereas neutrons which do not carry a charge interact with lighter elements, particularly hydrogen, and also carbon and oxygen, i.e. with elements of which synthetic plastic materials are generally composed or which at least form a very substantial part of the synthetic plastic materials.

Upon such contact, elastic and nonelastic collisions occur which reduce the kinetic energy of the neutrons, and collisions which cause absorption and possibly the formation of beta, gamma, and ionic radiation.

By incorporating the above-mentioned fatty acid compounds into the polymeric material, the number of hydrogen atoms available for slowing down and absorption of neutrons is greatly increased whereas the heavy metals will absorb the impinging or formed gamma rays. This is particularly important in the case of synthetic materials since radiation thereof tends to reduce and impair their mechanical properties or even to destroy the same. The radiation protection by means of synthetic materials, in the form of plates, blocks, sheets, lacquer coatings and the like, is important particularly since some of these polymeric materials can be intimately and firmly bound to concrete, steel, iron, aluminum and the like, whereas the resilient polymeric materials, particularly the natural and synthetic rubbers, due to their flexibility and/or resiliency, are highly useful for producing protective clothing, such as aprons, thereof.

It has been found, however, that the desired results are achieved to a satisfactory extent only with a certain group of plastic materials, partially because the fatty acid compounds cannot be incorporated or can only be difficulty incorporated into certain plastic materials, and partially because some of the plastic materials will be so much reduced in their mechanical properties, such as tear and bending resistance when exposed to alpha, beta, gamma, ionic or neutron radiations that the materials become brittle or are destroyed.

For these reasons, the present invention is generally not concerned with improving the shielding effect of cellulose esters and ethers, polycarbonates, silicone resins, polymethylene oxide resins, phenolic resins galalith and vulcanized fibers.

On the other hand, the present invention is excellently suitable for producing a shielding effect by incorporating the fatty acid compounds described above into polyurethanes, polyamides, polyethylene, polyfluoroethylene, polypropylene, epoxy resins, unsaturated polymerizable polyesters, and natural and synthetic rubbers.

Furthermore, good results, although sometimes not quire as good as those which are achieved with the group of polymeric materials mentioned above, may also be obtained with polyvinyl chloride, polyvinyl fluoride, copolymers thereof, polystyrene and copolymers thereof and methacrylate resins.

Of the synthetic rubbers, it is particularly preferred to utilize polyisobutylene, and good results were also obtained with butadiene-styrene and polymerizates, chloroprene and alkylpolysulfides.

The proportion of metal-fatty acid compounds relative to the synthetic polymeric materials or rubbers (natural or synthetic) depends on the specific polymeric materials and the specific fatty acid compounds which are utilized, and generally will equal between about 5 and 60 percent of the weight of the finished product, and preferably between and 40 percent thereof.

Upon working up of the mixtures on extrusion devices or calenders, the metal-fatty acid compounds will simultaneously serve as stabilizing lubricants and, in the case of rubbers, for increasing the resiliency thereof so that for instance the incorporation of relatively very large proportions of lead powder is possible while still maintaining the desired resilient characteristics of the material. These advantages are obtainable particularly with respect to the two last mentioned groups of preferred and utilizable polymeric materials whether they are natural rubbers or synthetic polymers.

By further additions of pulverulent lead and its compounds, for instance lead oxides or lead sulfide but also others, tungsten and its oxides, iron and its oxides, preferably in finely pulverulent or colloidal form, the shielding effect against gamma rays will be increased, whereas the additional incorporation of boron compounds, preferably boron trioxide, boron carbide, boron carbide-aluminum, and carbon nitride, as well as cadmium and cadmium compounds, for instance cadmium oxide and cadmium sulfide, will increase the absorption of the decelerated neutrons. Boron may also be utilized in the form of boric acid esters such as glycerol boric acid ester, combined with or together with stearic acid. The proportion of such additional pulverulent or colloidal additives relative to the proportion of the metal-fatty acid compounds will again depend on the specific type of the natural rubber synthetic polymeric material as well as the degree of shielding effect required and the desired mechanical strength and characteristics of the rubber or synthetic polymeric material. Generally, the proportions of these pulverulent additives of preferably colloidal dimensions, may be the same or even greater than the percentage of the metal fatty acid compounds.

The shaped bodies having a shielding effect, which are obtainable according to the present invention, may be prepared by introducing the metal-fatty acid compounds and possibly the further additives described above into the polymerizable synthetic materials, or the natural rubber, while the latter are in liquid form, and thereafter causing polymerization of the polymerizable fraction of the thus-formed mixture. In the case of natural and synthetic rubbers, the addition of the metalfatty acid compounds and, if desired, the further additive is preferably carried out during vulcanization or mastication.

The following examples are given as illustrative only without, however, limiting the invention to the specific details of the examples.

EXAMPLE I 100 parts by weight epoxy resin are mixed in a heated stir ring device with 50 parts by weight lead stearate and 50 parts by weight lead of finely pulverulent to colloidal size. Mixing is carried out at 125 C., and thereafter parts by weight of hexahydrophthalic acid are added.

After thorough mixing, the thus-formed mixture is cast into plates having a thickness of 20 mm.

EXAMPLE 2 parts by weight epoxy resin are mixed in a heatable stirring device with 20 parts by weight of lead stearate, 10 parts by weight of finely subdivided or colloidal lead powder and 10 parts by weight boron trioxide. The mixing is carried out at 1 10 C. Thereafter, ll parts by weight diethylene triamine are incorporated into the mixture and the latter then poured onto steel plates.

EXAMPLE 3 100 parts of granulated polyethylene having an edge length of 3-4 mm. and a density of 0.93 are intimately mixed with 20 parts by weight cadmium stearate and -7 parts by weight boron carbide and the thus formed mixture is then molten under pressure in a heated mold at l30l35 C. and compressed into plates having a thickness of 60 mm. After cooling, the plates are removed from the mold.

EXAMPLE 4 100 parts of unsaturated polyester resin which is formed of saturated and unsaturated dicarboxylic acids with divalent alcohol in molar relationship and dissolved with 25 percent styrene and 5 percent allylethers of polyvalent alcohols, are mixed with 30 parts by weight lead stearate and 10 parts by weight butylacetate. Thereafter 0.5 parts by weight benzoyl peroxide and 0.05 parts by weight of cobalt naphthenate are admixed.

After thorough mixing, the entire mixture is applied to a support in the form of a lacquer layer having a thickness of 4 EXAMPLE 5 100 parts by weight chloroprene, for instance the type commercially available as Neoprene AC" are calendered on a heatable calender. Over a period of 10 minutes there are added in the indicated sequence:

2.5 parts by weight active zinc oxide, 300 parts by weight lead montanate, 20.0 parts by weight colloidal lead powder, and 3.0 parts by weight of boron trioxide.

Calendering is carried out until a uniform mixture is obtained, and to the desired thickness.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended:

1. A shaped body having a shielding effect against radioactive radiation, particularly gamma and neutron radiation, said shaped body consisting essentially of a material selected from the group consisting of natural and synthetic rubbers and synthetic plastic materials, having distributed therethrough and intimately mixed therewith an effective amount of at least one compound of a saturated fatty acid being solid at room temperature and having at least 9 carbon atoms with at least one metal selected from the group consisting of lead, bismuth, tungsten, zirconium, ion, tin, cadmium, lithium and barium.

2. A shaped body as defined in claim 1, and additionally including a boron compound.

3. A shaped body as defined in claim 2, wherein the content of said boron compound is in the range from about 3 to parts by weight relative to 100 parts by weight of said material.

4. A shaped body as defined in claim 1, wherein said material is selected from the group consisting of polyurethane, polyamide, polyethylene, polyfluoroethylene, polypropylene, epoxy resins, unsaturated polymerizable polyesters, and natural and synthetic rubbers.

5. A shaped body as defined in claim 1, wherein the material is selected from the group consisting of polyvinyl chloride, polyvinyl fluoride, copolymers of polyvinyl fluoride and polyvinyl chloride, polystyrene and copolymers thereof, and polymethacrylates.

6. A shaped body as defined in claim 1, wherein said material is a synthetic rubber selected from the group consisting of chloroprene, butadiene-styrcne polymerizates, polyisobutylene and alkyl-polysulfides.

7. A shaped body as defined in claim 1, wherein said effective amount is equal to between 5 and 60 percent of the weight of said shaped body.

8. A shaped body as defined in claim 7, wherein said effective amount is equal to between 10 and 40 percent of the weight of said shaped body.

9. A shaped body as defined in claim 1, and additionally including an effective amount of at least one finely subdivided substance selected from the group consisting of lead and lead compounds, tungsten and tungsten oxides, iron and iron compounds, boron and boron compounds, cadmium, cadmium oxide and cadmium sulfide.

10. A shaped body as defined in claim 9, wherein the particles of said additional finely subdivided substance are of colloidal dimensions.

11. A shaped body as defined in claim 9, wherein said boron compound is selected from the group consisting of boron carbide, boric acid and boron trioxide.

12. A shaped body as defined in claim 1, wherein said shaped body is a plate.

13. A shaped body as defined in claim 1, wherein said shaped body is a coating.

14. A shaped body as defined in claim 1, wherein said shaped body is a flexible sheet. 

2. A shaped body as defined in claim 1, and additionally including a boron compound.
 3. A shaped body as defined in claim 2 wherein the content of said boron compound is in the range from about 3 to 10 parts by weight relative to 100 parts by weight of said material.
 4. A shaped body as defined in claim 1, wherein said material is selected from the group consisting of polyurethane, polyamide, polyethylene, polyfluoroethylene, polypropylene, epoxy resins, unsaturated polymerizable polyesters, and natural and synthetic rubbers.
 5. A shaped body as defined in claim 1, wherein the material is selected from the group consisting of polyvinyl chloride, polyvinyl fluoride, copolymers of polyvinyl fluoride and polyvinyl chloride, polystyrene and copolymers thereof, and polymethacrylates.
 6. A shaped body as defined in claim 1, wherein said material is a synthetic rubber selected from the group consisting of chloroprene, butadiene-styrene polymerizates, polyisobutylene and alkyl-polysulfides.
 7. A shaped body as defined in claim 1, wherein said effective amount is equal to between 5 and 60 percent of the weight of said shaped body.
 8. A shaped body as defined in claim 7, wherein said effective amount is equal to between 10 and 40 percent of the weight of said shaped body.
 9. A shaped body as defined in claim 1, and additionally including an effective amount of at least one finely subdivided substance selected from the group consisting of lead and lead compounds, tungsten and tungsten oxides, iron and iron compounds, boron and boron compounds, cadmium, cadmium oxide and cadmium sulfide.
 10. A shaped body as defined in claim 9, wherein the particles of said additional finely subdivided substance are of colloidal dimensions.
 11. A shaped body as defined in claim 9 wherein said boron compound is selected from the group consisting of boron carbide, boric acid and boron trioxide.
 12. A shaped body as defined in claim 1 wherein said shaped body is a plate.
 13. A shaped body as defined in claim 1 wherein said shaped body is a coating.
 14. A shaped body as defined in claim 1 wherein said shaped body is a flexible sheet. 